When you're buying a webhosting package, you might be wondering if the bandwidth allowance advertised is enough for your website.

The Bandwidth Allowance is the total amount of data in Gigabytes (GB) that you can transfer into and out of the web server per month.
bandwidth allowance on hosting plan

Let's Calculate Bandwidth

You need to get 3 figures to do this calculation:

  1. Average size of your webpages - find this out by putting the website url into https://www.webpagetest.org/
  2. Number of Visitors to website/day - find this in Google Analytics
  3. Average number of pages that visitors view - find this in Google Analytics (average pageviews)

Some Examples

For easy comparison, I'll keep the average page size and average page views the same for all four types of website. I'll add a safety factor of 1.2 at the end because data transfer counts both in and out of the server, not just webpages served to visitors (which is out only).

data calcs Small Average Large Busy
  50 100 1000 10000
  3.5 3.5 3.5 3.5
Avg Page size (kB)
  120 120 120 120
Data/day (kB)
=A*B*C 21000 42000 420000 4200000
Data/day (GB)
=D/1000000 0.021 0.042 0.42 4.2
=E*30 0.63 1.26 12.6 126
Safety Factor
=F*1.2 0.756 GB/mo 1.512 GB/mo 15.12 GB/mo 151.2 GB/mo

It's been estimated that 99% of websites use less than 5GB/month in data transfer

The Truth about Bandwidth

To understand the truth about Bandwidth, you need to understand how web hosts pay their suppliers for data. There are 2 important points here.

  1. Webhosts pay their suppliers for every single Gigabyte (GB) of data processed and transferred in/out of their servers.
  2. Webhosts also agree a figure for bandwidth with their suppliers and will suffer penalties if this bandwidth cap is breached.

The bandwidth cap that webhosts are bound by is not about the amount of data per month, as they advertise to you, but the maximum amount of data that can flow per second, which is measured in Gigabits (not bytes) per second, or Gbps. A breach of the bandwidth cap comes with financial penalties for the webhost.

Bandwidth - the real definition - is the maximum amount of data that can be transferred per second

What are the Implications?

Web hosts are offering more and more Bandwidth Allowance to their customers to draw them in. Faced with a 10GB monthly allowance, or an Unlimited monthly allowance for data transfer, which would you pick?

Most people would go for Unlimited because they believe it will make their website faster. After all, the more data that can flow, the faster it must be, right?

WRONG! Remember point 2. above? Webhosts have a pre-agreed cap on bandwidth with their suppliers! And that's real bandwidth, defined as the maximum amount of data that can flow per second.

Unlimited Bandwidth

Unlimited Bandwidth is the ultimate myth. There is no such thing. Bandwidth is capped and data flowing must be paid for by the webhost. So how do they do it?

Easy. They are banking on the fact that the majority of websites on the server will use less than 5GB data per month, and (this is important), that they will use that data evenly throughout the month.

Webhosts cannot afford to breach their own bandwidth cap, so the last thing they want is a website that frequently uses data in large 'spikes'. This could happen on a Black Friday weekend, or after a heavy advertising campaign for instance. Spikes are a threat to the bandwidth cap. When that happens, your website (or even the entire server) will be 'throttled' - slowed down - until the spike is over. If a website continues spiking, the webhost will suggest a higher data plan which has a higher bandwidth cap built in.

What about the Cost of Unlimited Data?

Again it's a numbers game. Webhosts are relying on the fact that only a very small percentage of websites on a shared server are using more than 5GB of data in a month. At an average cost of, let's say 0.08c/GB, that would cost the webhost just $40 for 100 websites.

That cost doubles to around $80 if just 5% of those websites consume 100GB/mo. So they can afford to allow a small percentage to use up more data.

To put that into perspective, if all 100 websites used 100Gb/mo the cost to the webhost would be $800! Given their clients might be paying $5/mo for a shared webhosting package, that would represent a monthly loss of $300.

Unmetered Bandwidth

If you ever see a plan billed as Unmetered Bandwidth, don't think for a moment that you're not being metered. You sure are.

An unmetered plan means there is a hard cap on the amount of data that you can use in a second - ie a real bandwidth cap, not a balancing act like Unlimited Bandwidth.

A driving analogy works well to understand this one:

You go to the car dealer who has advertised UNLIMITED MILEAGE and you can drive as long as you like for a month. However, what you don't know is that the car's speed is capped at 90km/h. Therefore, your top distance can only be 90km/h x 24h x 30days which is a maximum distance of 64800km (and that's without meals, sleep or bathroom breaks).

Unmetered bandwidth caps the rate of data transfer per second, which is such a clever way of capping the amount of data that you can actually use.

The Bottom Line

Webhosts don't publicise the bandwidth caps of their shared servers. The only place you're likely to find a semblance of an explanation is in the webhost's AUP (Acceptable Usage Policy) and the following wording would not be untypical:

  • We reserve the right to limit your bandwidth if it impacts our server or clients negatively. Your site may become unreachable at this time.
  • You will agree to pay for bandwidth usage over and above the stated bandwidth of the server.

The problem you face is that the stated bandwidth of the server is not actually stated anywhere. So if you don't know what the maximum rate of data transfer is, then you can't actually calculate how much you can (really) use or at what rate of usage your website gets throttled. Do you get throttled, or does the entire server get throttled? The last thing you need on that busy Black Friday weekend is your website slowing down to a crawl.

If your website is devouring 100GB/mo plus of data, and you have heavy traffic spikes, then the truth is you shouldn't be on a shared web hosting plan. Shared means shared. You're sharing the bandwidth with all the other tenants on the server. Analyse your traffic and talk to your webhost about a better plan for your needs. 

If, on the other hand, your website is using 5GB/mo of data or less, and your traffic is pretty evenly spread, then you should feel more than comfortable on a plan offering 10GB of monthly data usage.